This invention relates to a brake shoe having an arcuate platform carrying a lining of friction material and intended for use in an internal shoe drum brake, primarily for a motor vehicle, and of the kind having a pair of brake shoes mounted on a back plate and separable by an actuator into braking engagement with a rotary brake drum. The invention also embraces an internal shoe drum brake incorporating a plurality of brake shoes.
Problems during bedding in new brake linings against the braking surface of a rotary brake drum are often due to the occurrence of random high spots on the linings which can give rise, during the bedding in process, to local areas of excessive loading, leading potentially to uneven braking, and/or drum distortion and its resultant brake judder. These problems can occur despite the fact that new linings are often ground to match generally the drum curvature, because production tolerances result in the contact areas of the linings being ill-defined or spaced unevenly around the drum circumference.
The invention is a brake shoe for an internal shoe drum brake, and a drum brake containing a plurality of such shoes, in which the aforesaid problems are alleviated or avoided, by controlling accurately the formation of the lining to drum contact areas and spacing these areas as evenly as possible around the drum circumference.
According to the invention, a brake shoe comprises an arcuate platform carrying a lining of friction material, the lining having, at or adjacent its outer ends, localised portions projecting radially outwardly beyond the remainder of the lining.
The lining may conveniently be in three separate sections, of which the two outermost ones preferably have convex projecting surfaces having radii of curvature which are, typically, smaller than that of the remaining lining.
With the arrangement of the invention, the sections of lining providing the initial areas of contact between the lining and drum are spaced in a generally balanced manner around the drum, which greatly reduces the risk of drum distortion and resultant brake judder.